Method of producing nanopatterned articles, and articles produced thereby

ABSTRACT

A nanopatterned surface is prepared by forming a block copolymer film on a miscut crystalline substrate, annealing the block copolymer film, then reconstructing the surface of the annealed block copolymer film The method creates a well-ordered array of voids in the block copolymer film that is maintained over a large area. The nanopatterned block copolymer films can be used in a variety of different applications, including the fabrication of high density data storage media.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. Nonprovisional patent applicationSer. No. 13/461,175 filed May 1, 2012, which is a division of U.S.Nonprovisional patent application Ser. No. 12/553,401 filed Sep. 3,2009, which claims the benefit of U.S. Provisional Patent ApplicationSer. No. 61/098,253 filed Sep. 19, 2008. Each of these priorityapplications is fully incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH & DEVELOPMENT

This invention was made with government support under MRSEC on PolymersGrant No. DMR-0213695 awarded by the National Science Foundation, andOffice of Basic Energy Sciences Grant No. DE-FG02-96ER45612 awarded bythe Department of Energy. The government has certain rights in theinvention.

BACKGROUND OF THE INVENTION

For nanotechnological applications, the use of thin films of materialsis highly preferred. See, for example, R. A. Segalman, Materials Scienceand Engineering, 2005, volume R48, page 191 ff.; M. Li and C. K. Ober,Materials Today, 2006, volume 9, page 30 ff.; C. J. Hawker and T. P.Russell, MRS Bulletin, 2005, volume 30, page 952 ff.; and M. Li, C. A.Coenjarts, and C. K. Ober, Advances in Polymer Science, 2005, volume190, page 183 ff. It would be desirable, in the case of block copolymers(BCPs), to have the nanoscopic domains, sometimes referred to asmicrodomains, oriented in a specific direction with a long-range lateralorder for applications such as polarizers (see, for example, V.Pelletier, K. Asakawa, M. Wu, D. H. Adamson, R. A. Register, and P. M.Chaiken, Applied Physics Letters, 2006, volume 88, page 211114 ff.),templates for pattern transfer to generate microelectronic integratedcircuits (see, for example, C. T. Black, IEEE Transactions onNanotechnology, 2004, volume 3, page 412 ff.), magnetic media (see, forexample, C. A. Ross, Annual Review of Materials Research, 2001, volume31, page 203 ff.), and optical waveguides (see, for example, C. A. Ross,Annual Reviews of Materials Research, 2001, volume 31, page 203 ff.; andS. A. Maier, M. L. Brongersma, P. G. Kik, S. Meltzer, A. A. G. Requicha,and H. A. Atwater, Advanced Materials, 2001, volume 13, page 1501 ff.).In recent years, a number of approaches have been developed to controlthe orientation and enhance the lateral order of the microdomains byapplying external fields, such as electric fields (see, for example, T.Thurn-Albrecht, J. DeRouchey, and T. P. Russell, Macromolecules, 2000,volume 33, page 3250 ff.), shear (see, for example, M. A. Villar, D. R.Rueda, F. Ania, and E. L. Thomas, Polymer, 2002, volume 43, page 5139ff.), temperature gradients (see, for example, J. Bodycomb, Y. Funaki,K. Kimishima, and T. Hashimoto, Macromolecules, 1999, volume 32, page2075 ff.), graphoepitaxy (see, for example, R. A. Segalman, H. Yokoyama,and E. J. Kramer, Advanced Materials, 2001, volume 13, page 1152 ff.),chemically patterned substrates (see, for example, M. P. Stoykovich, M.Müller, S. O. Kim, S. O.; Solak, H. H.; Edwards, E. W.; de Pablo, J. J.;Nealey, P. F. Science 2005, volume 308, page 1442 ff.), controlledinterfacial interactions (see, for example, P. Mansky, Y. Liu, E. Huang,T. P. Russell, and C. J. Hawker, Science, 1997, volume 275, page 1458ff.; and E. Drockenmuller, L. Y. T. Li, D. Y. Ryu, E. Harth, T. P.Russell, H. C. Kim, and C. J. Hawker, Journal of Polymer Science, PartA: Polymer Chemistry, 2005, volume 43, page 1028 ff.), zone casting(see, for example, C. Tang, A. Tracz, M. Kruk, R. Zhang, D.-M. Smilgies,K. Matyjaszewski, and T. Kowalewski, Journal of the American ChemicalSociety, 2005, volume 127, page 6918 ff.), optical alignment (see, forexample, Y. Morikawa, S. Nagano, K. Watanabe, K. Kamata, T. Iyoda, andT. Seki, Advanced Materials, 2006, volume 18, page 883 ff.), solventfields (see, for example, G. Kim and M. Libera, Macromolecules, 1998,volume 31, page 2569 ff.; M. Kimura, M. J. Misner, T. Xu, S. H. Kim, andT. P. Russell, Langmuir, 2003, volume 19, page 9910 ff.; S. Ludwigs, A.Böker, A. Voronov, N. Rehse, R. Magerle, and G. Krausch, G. NatureMaterials, 2003, volume 2, page 744 ff.; S. H. Kim, M. J. Misner, T. Xu,M. Kimura, and T. P. Russell, Advanced Materials, 2004, volume 16, page226 ff.; R.-M. Ho, W.-H. Tseng, H.-W. Fan, Y.-W. Chiang, C.-C. Lin,B.-T. Ko, and B.-H. Huang, Polymer, 2005, volume 46, page 9362 ff.; Z.Lin, D. H. Kim, X. Wu, L. Boosanda, D. Stone, L. LaRose, and T. P.Russell, Advanced Materials, 2002, volume 14, page 1373 ff.; J. Hahm andS. J. Sibener, Langmuir, 2000, volume 16, page 4766 ff.; and S. Park, B.Kim, J.-Y. Wang, and T. P. Russell, Advanced Materials, 2008, volume 20,page 681 ff.), and so on. Solvent evaporation is a strong and highlydirectional field. Making BCP thin films under various solventevaporation conditions has been found to be a good way to manipulate theorientation and lateral ordering of BCP microdomains in thin films Kimet al. first reported that solvent evaporation could be used to inducethe ordering and orientation of BCP microdomains. G. Kim and M. Libera,Macromolecules, 1998, volume 31, page 2569 ff. Vertically alignedcylindrical polystyrene microdomains could be obtained inpolystyrene-b-polybutadiene-b-polystyrene triblock copolymer thin filmswith a thickness of about 100 nanometers. The same effect was alsoobserved in polystyrene-b-poly(ethylene oxide) (PS-b-PEO) andpolystyrene-b-poly(L-lactide) BCP thin films and was attributed to acopolymer/solvent concentration gradient along the direction normal tothe film surface giving rise to an ordering front that propagated intothe film during solvent evaporation. R.-M. Ho, W.-H. Tseng, H.-W. Fan,Y.-W. Chiang, C.-C. Lin, B.-T. Ko, and B.-H. Huang, Polymer, 2005,volume 46, page 9362 ff.; Z. Lin, D. H. Kim, X. Wu, L. Boosanda, D.Stone, L. LaRose, and T. P. Russell, Advanced Materials, 2002, volume14, page 1373 ff. This orientation was independent of the substrate.However, the lateral ordering of the cylindrical microdomains was poor.Hahm et al. and later Kimura et al. showed that evaporation-induced flowin solvent cast BCP films produced arrays of nanoscopic cylindersoriented normal to the surface with a high degree of ordering. J. Hahmand S. J. Sibener, Langmuir, 2000, volume 16, page 4766 ff.; and M.Kimura, M. J. Misner, T. Xu, S. H. Kim, and T. P. Russell, Langmuir,2003, volume 19, page 9910 ff. Recently, Ludwigs et al. demonstratedthat solvent annealing could markedly enhance the ordering of BCPmicrodomains in thin films S. Ludwigs, A. Böker, A. Voronov, N. Rehse,R. Magerle, and G. Krausch, G. Nature Materials, 2003, volume 2, page744 ff. By controlling the rate of solvent evaporation and solventannealing in thin films of PS-b-PEO, Kim et al. achievednearly-defect-free arrays of cylindrical microdomains oriented normal tothe film surface that spanned the entire films S. H. Kim, M. J. Misner,T. Xu, M. Kimura, and T. P. Russell, Advanced Materials, 2004, volume16, page 226 ff. Moreover, the use of a co-solvent enabled furthercontrol over the length scale of lateral ordering. The most recentresults showed that perpendicular cylindrical microdomains orientednormal to the film surface could be obtained directly by spin-coatingpolystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) BCPs from mixed solventsof toluene and tetrahydrofuran (THF) and arrays of highly orderedcylindrical microdomains formed over large areas after exposing thefilms in the vapor of a toluene/THF mixture. This process wasindependent of substrate, but strongly depended on the quality of thesolvents for each block and the solvent evaporation rate. S. Park, J.-Y.Wang, B. Kim, W. Chen, and T. P. Russell, Macromolecules 2007, volume40, page 9059 if But, the ultimate achievable data storage densityachievable with these BCPs will not exceed 1 terabit per square inch(Tbit/in²). Processes to use alternate BCPs, like PS-b-P4VP or PS-b-PEOcontaining salt, have been developed that are simpler to employ and,more importantly, the interactions between the segments of the copolymerare very non-favorable, making defects energetically costly and, also,opening an avenue to smaller domain sizes and separation distances. S.H. Kim, M. J. Misner, L. Yang, O. Gang, B. M. Ocko, T. P. Russell,Macromolecules 2006, volume 39, page 8473 ff.

Several methods have been developed to prepare nearly perfect patternsin polymer surfaces on substrates. Conventional photolithography,electron beam (e-beam) lithography, and scanning force probe lithographyare accessible techniques for fabrication of nanometer-size patterns.For example, Schmidt and co-workers showed the successfulelectrochemical modification of self-assembled monolayers at positionswhere a conductive scanning probe was in contact with a self-assembledmonolayer. D. Wyrwa, N. Beyer, and G. Schmid, G. Nano Letters, 2002,volume 2, page 419 ff. The induced chemical contrast was used to guidethe covalent binding of Au crystals from solution. E-beam lithography isa common method for fabrication of sub-micrometer structures. Although abeam of electrons may be focused to less than 1 nanometer in diameter,the resolution is limited by the interaction of the beam with the resistmaterial and by the radius of gyration of the macromolecules, which isusually a few nanometers. See, for example, J. M. Gibson, Physics Today,1997, volume 50, page 56 ff. New developments in using self-assembledmonolayers overcome these restrictions inherent with standard resistmaterials as their thickness is usually a few angstroms. Structures assmall as a few nanometers were fabricated by using this concept. See,for example, A. Gölzhäuser, W. Eck, W. Geyer, V. Stadler, T. Weimann, P.Hinze, and M. Grunze, Advanced Materials, 2001, volume 13, page 806 ff.;R. Glass, M. Arnold, E. A. Cavalcanti-Adam, J. Blümmer, C. Haferkemper,C. Dodd, and J. P. Spatz, New Journal of Physics, 2004, volume 6, page101 ff.; and S.-M. Yang, S. G. Jang, D.-G. Choi, U.S. Pat. No. 7,081,269B2 (2006). However, these approaches require expensive equipment andhigh-energy doses, and they are not suitable for non-conductivesubstrates unless additional treatment is carried out. Moreover, e-beampatterning is a time-consuming serial process not suitable for largeareas.

It is highly desirable to develop parallel processes where thesequential generation of nanoscopic features is avoided and thepatterning is achieved in one step. Nanoimprint lithography (NIL) is onesuch process to control the positional order of the microphase separatedmorphology. NIL can be used for locally controlling the self-assemblyprocess of block copolymers and determining the precise positioning ofthe phase-separated domains via the topography of mold, rather than thesubstrate. NIL creates features by a mechanical deformation of a polymerfilm by pressing a hard mold into the film at temperatures higher thanthe glass transition temperature of the polymer. This high-throughput,low cost process is not diffraction limited, and sub-10 nanometerresolution has been reported. See, for example, S. Y. Chou, P. R.Krauss, W. Zhang, L. Guo, and L. Zhuang, Journal of Vacuum Science andTechnology B, 1997, volume 15, page 2897 ff.; H.-W. Li and W. T. S.Huck, Nano Letters, 2004, volume 4, page 1633 ff.; S. Y. Chou, U.S. Pat.No. 5,772,905 (1998); and J.-H. Jeong, H. Sohn, Y.-S. Sim, Y.-J. Shin,E.-S. Lee, and K.-H. Whang, U.S. Pat. No. 6,943,117 B2 (2005). Yet, NILhas the limitation that it requires a master that is used for theprinting and, as of yet, it has not been possible to generate a perfectmaster with uniform, nanoscopic features sizes less than 20 nanometersover large lateral distances while maintaining the features in register.

BRIEF DESCRIPTION OF THE INVENTION

The present invention utilizes the perfect crystal ordering of acrystalline substrate, like single crystal silicon, to produce atopographic patterning of a surface of the substrate that in turn guidesthe placement of the nanoscopic features in a block copolymer filmformed on the patterned surface of the substrate. For example, miscutsilicon single crystals can be used to produce large areas of saw-toothlike surface morphologies. A characteristic lateral spacing betweentopological features of less than 100 nanometers can be achieved oversurface areas of centimeter-squared dimensions. The combination ofsubstrate-induced block copolymer morphology and solvent annealing ofblock copolymer thin films can be used to fabricate nanoporous templatesor scaffolds having feature sizes of about 5 nanometers over an entirewafer of arbitrary size. The process is compatible with existingfabrication technologies and is, therefore, nondisruptive.

One embodiment is a method of preparing a nanopatterned surface,comprising: forming a block copolymer film on an annealed, miscutsurface of a crystalline substrate; annealing the block copolymer film;and surface reconstructing the annealed block copolymer film

Another embodiment is a layered article prepared by the process.

These and other embodiments are described in detail below.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic illustration of articles associated with thepresent method; FIG. 1(A) shows the substrate 1; FIG. 1(B) shows theblock copolymer film-coated substrate 10; FIG. 1(C) shows the annealedblock copolymer film-coated substrate 20; FIG. 1(D) shows thesolvent-reconstructed, annealed block copolymer film-coated substrate30.

FIG. 2 is a schematic illustration of articles associated with a methodfor forming a nanopatterned substrate; FIG. 1(A) shows thesolvent-reconstructed, annealed block copolymer film-coated substrate30; FIG. 1(B) shows the resist-coated, solvent-reconstructed, annealedblock copolymer film-coated substrate 40; FIG. 1(C) shows the etched,resist-coated, solvent-reconstructed, annealed block copolymerfilm-coated substrate 50.

FIG. 3 is a scanning force microscope (SFM) image of a 5 micrometer×5micrometer area of an annealed crystalline aluminum oxide substrate.

FIG. 4. is an SFM image of a 4 micrometer×4 micrometer area of apolystyrene-block poly(ethylene oxide) (PS-b-PEO) block copolymer thinfilm annealed in solvent vapor on a thermally annealed crystallinealuminum oxide (sapphire) substrate; the polystyrene block numberaverage molecular weight was about 20,000 atomic mass units, and thepoly(ethylene oxide) block number average molecular weight was about6,500 atomic mass units; the inset is a Fourier transform image of thecylindrical microdomains.

FIG. 5. is an SFM image of a 2 micrometer×2 micrometer area of aPS-b-PEO thin film annealed in solvent vapor on a thermally annealedcrystalline aluminum oxide (sapphire) substrate; the polystyrene blocknumber average molecular weight was about 16,000 atomic mass units, andthe poly(ethylene oxide) block number average molecular weight was about3,500 atomic mass units; the inset is a Fourier transform image of thecylindrical microdomains.

FIG. 6 shows silicon oxide surface with nano-sized pores (A), andnano-sized pillars (B).

FIG. 7 shows an annealed polystyrene-block-poly(ethylene oxide) film ona miscut sapphire substrate; the film was annealed in xylene vapor for 2hours at room temperature.

FIG. 8 shows Moire patterns on annealed polystyrene-block-poly(ethyleneoxide) films on flat M-plane sapphire (FIG. 8(A); unpatterned surface)and miscut sapphire (FIG. 8(B); patterned surface) substrates.

FIG. 9 shows two dimensional GISAXS patterns of PS-b-PEO thin films;FIG. 9(A) represents the hexagonal cylinder viewed from the direction ofcylindrical axes, the (10) symmetric plane; FIG. 9(B) was obtained whenthe sample stage was rotated to 30 degrees from the (10) symmetricplane.

DETAILED DESCRIPTION OF THE INVENTION

One embodiment is a method of preparing a nanopatterned surface,comprising: forming a block copolymer film on an annealed, miscutsurface of a crystalline substrate; annealing the block copolymer film;and surface reconstructing the annealed block copolymer film. In thefirst step of the method, a block copolymer film is formed on anannealed, miscut surface of a crystalline substrate. The substratesurface provides a highly regular pattern of topographic features overlarge (at least centimeter) distances. In some embodiments, thecrystalline substrate consists essentially of a single crystal. In thiscontext, the phrase “consists essentially of” allows levels of dopantsand impurities that do not substantially detract from the regularity ofthe surface topology. One useful class of crystalline substratesincludes crystalline silicon and doped crystalline silicon. Anotheruseful class of crystalline substrates is crystalline aluminum oxides(which, in some forms, are known as “sapphire” or “corundum”).

As used herein the term “nanopatterned surface” refers to a surfacecomprising repeating chemical and/or topographical homogeneities thathave dimensions on the nanometer scale. In some embodiments, thenanopatterned surface is the top surface of the annealed block copolymerfilm (where “top” is interpreted in terms of a structure in which theblock copolymer film is on top of the topographically patterned surfaceof the polymeric replica). In these embodiments, the annealed blockcopolymer film can comprise chemical inhomogeneities in the form ofcylinders or stripes (lamellae) perpendicular to the plane of the film,or spheres, cylinders, or stripes parallel to the plane of the film. Inother embodiments, the nanopatterned surface is the top surface of astructure produced after further processing of the annealed blockcopolymer film. For example, the nanopatterned surface can be the topsurface of a block copolymer film produced by solvent reconstruction ofthe annealed block copolymer film. As another example, the nanopatternedsurface can be the top surface of a structure produced by coating aresist from a glancing angle onto the solvent-reconstructed, annealedblock copolymer film. As yet another example, the nanopatterned surfacecan be the product of depositing a magnetic material directly(perpendicularly) onto the top surface and into the pores of a structurethat is the product of solvent-reconstructing the block copolymer film,resist-coating the solvent-reconstructed block copolymer film, andetching the resist-coated block copolymer film to create voids in theunderlying polymeric substrate corresponding to the voids of thesolvent-reconstructed block copolymer film. In each of these examples,the nanopattern has dimensions corresponding to the dimensions of thecylinders, stripes, spheres, or lamellae of the annealed block copolymerfilm.

The block copolymer film is formed on an annealed surface of thecrystalline substrate. This means that the substrate has been heated toa temperature at which a regularly repeating surface topology is formed,then cooled to preserve that topology so that it is present under theconditions with which the block copolymer film is formed. For example,miscut silicon can be annealed by heating to a temperature ofapproximately 1262° C. for one minute, then rapidly cooling to 1027° C.,followed by slow cooling to room temperature. As another example, miscutC-plane sapphire can be annealed by heating in air at 1100° C. for 10hours, followed by cooling to room temperature.

The surface of the crystalline substrate on which the block copolymerfilm is formed is miscut. As used herein, the term “miscut” means thatthe crystalline surface is at least 1 degree removed from anycrystallographic plane of the crystalline substrate. In someembodiments, the crystalline surface is removed from anycrystallographic plane by 1 to 10 degrees, specifically 2 to 8 degrees,more specifically 3 to 6 degrees. It will be understood that the term“miscut” includes some crystalline surfaces, such as miscut sapphire,that are conventionally defined with reference to a surface normal(rather than the surface plane).

There is no particular limit on the topology of the annealed, miscutsurface. In some embodiments, the annealed, miscut surface of thecrystalline substrate exhibits a saw-tooth pattern. The saw-toothpattern can be characterized by a peak-to-peak separation of about 24 toabout 200 nanometers and a peak-to-valley separation of about 3 to about20 nanometers. Within the range of 24 to 200 nanometers, thepeak-to-peak separation can be 30 to 150 nanometers, specifically 40 to120 nanometers, more specifically 50 to 100 nanometers. Within the rangeof 3 to 20 nanometers, the peak-to-valley separation can be 5 to 18nanometers, specifically 8 to 15 nanometers.

In some embodiments, the annealed, miscut surface of the crystallinesubstrate exhibits a grooved pattern. The grooved pattern can becharacterized by a groove depth of about 3 to about 20 nanometers and agroove-to-groove separation of about 24 to about 200 nanometers. Withinthe range of about 3 to about 20 nanometers, the groove depth can be 5to 18 nanometers, specifically 8 to 15 nanometers. Within the range of24 to 200 nanometers, the groove-to-groove separation can be about 30 toabout 150 nanometers, specifically 40 to 120 nanometers, morespecifically 50 to 100 nanometers.

In some embodiments, the annealed, miscut surface of the crystallinesubstrate is chemically homogeneous. In other embodiments, the annealed,miscut surface of the crystalline substrate is chemically patterned. Oneexample of a chemically patterned surface is a surface comprisingstripes of oxide and metal. As background, see L. Rockford, Y. Liu, T.P. Russell, M. Yoon, and S. C. J. Mochrie, Physical Review Letters,1999, volume 82, page 2602 ff.

Methods of forming crystalline substrates with miscut, annealed surfacesare described in, for example, S. Song, S. G. J. Mochrie, and G. B.Stephenson, Physical Review Letters, 1995, volume 74, page 5240 ff.; andS. Song and S. G. J. Mochrie, Physical Review B, 1995, volume 51, page10068 ff. Specific procedures for forming annealed surfaces on miscutsilicon and sapphire are provided in the working examples below.

Once a crystalline substrate with an annealed, miscut surface isprepared, a block copolymer film is formed on the surface. In someembodiments, forming the block copolymer film comprises spin coating theblock copolymer film from solution onto the annealed, miscut surface ofthe crystalline substrate. For example, a solution comprising apolystyrene-poly(4-vinylpyridine) diblock copolymer in a mixture oftoluene and tetrahydrofuran can be spin coated onto crystalline siliconor crystalline aluminum oxide.

In order to form at least two domains in the block copolymer film, theblock copolymer should comprise at least two chemically distinct blocks.There is no particular limitation on the chemical composition of theblock copolymer blocks, provided that block copolymer comprises a firstblock and second block that are sufficiently incompatible with eachother to form separate phases. Incompatibility of the two blocks can becharacterized by a difference in the Hildebrand solubility parameters ofthe two blocks. For example, when the block copolymer comprises a firstblock having a first Hildebrand solubility parameter and a second blockhaving a second Hildebrand solubility parameter, the first Hildebrandsolubility parameter and the second Hildebrand solubility parameter candiffer by at least 0.4 megapascal^(1/2).

In some embodiments, the block copolymer comprises at least one blockselected from the group consisting of polyolefins, poly(alkenylaromatic)s, poly(conjugated dienes)s, hydrogenated poly(conjugateddienes)s, poly(vinyl-substituted nitrogen heterocycle)s, poly(alkyl(meth)acrylate)s, poly((meth)acrylic acid)s, poly(alkylene oxide)s,poly(arylene oxide)s, poly(arylene sulfide)s, poly(vinyl alkanoates),poly(vinyl ether)s, poly(vinyl halide)s, poly(vinyl alcohol)s,polyurethanes, poly(meth)acrylonitriles, polyesters, polyamides,polyimides, polycarbonates, polysulfones, and polysiloxanes.

In some embodiments, the block copolymer comprises a poly(alkenylaromatic) block that is the polymerization product of an alkenylaromatic monomer having the structure

wherein R¹ is hydrogen or C₁-C₆ alkyl, and each occurrence of R², R³,R⁴, R⁵, and R⁶ is independently selected from the group consisting ofhydrogen, C₁-C₆ alkyl, and halogen. In some embodiments, the blockcopolymer comprises a polystyrene block.

In some embodiments, the block copolymer comprises apoly(vinyl-substituted nitrogen heterocycle) block that is thepolymerization product of a vinyl-substituted nitrogen heterocycleselected from the group consisting of 2-vinylpyridine, 3-vinylpyridine,4-vinylpyridine, 2-methyl-5-vinylpyridine 1-vinylimidazole,2-vinylimidazole, 4-vinylimidazole, N-vinyl-2-methylimidazole,N-vinyl-2-ethylimidazole, 2-vinylpyrrole, 3-vinylpyrrole, and mixturesthereof In some embodiments, the block copolymer comprises apoly(4-vinylpyridine) block or a poly(2-vinylpyridine) block.

The block copolymer can comprise the first block and the second block ina volume ratio of about 1:10 to about 10:1.

In some embodiments, the molecular weight of the first block issubstantially larger than the molecular weight of the second block. Forexample, the first block and the second block can differ in numberaverage molecular weight by at least a factor of 1.5, specifically afactor of 1.5 to 6, more specifically a factor of 2 to 5, still morespecifically a factor of 3 to 4.

In a very specific embodiment, the block copolymer is apolystyrene-poly(4-vinylpyridine) or polystyrene-poly(2-vinylpyridine)diblock copolymer. In another very specific embodiment, the blockcopolymer is a polystyrene-poly(ethylene oxide) diblock copolymer.

The block copolymer film typically has a thickness of about 10 to about100 nanometers. In some embodiments, the block copolymer film has athickness corresponding to about one period of the block copolymer. Therelationship between film thickness and the period of the blockcopolymer can be determined using methods known in the art. See, forexample, T. P. Russell, P. Lambooy, J. G. Barker, P. D. Gallagher, S. K.Satija, G. J. Kellogg, and A. M. Mayes, Macromolecules 28, 787 (1995);and A. M. Mayes, S. K. Kumar, MRS Bulletin, volume 22, page 43 ff.(1997).

Once the block copolymer film is formed, it is annealed. In someembodiments, the block copolymer film is thermally annealed. Forexample, when the block copolymer is a polystyrene-block-poly(n-butylmethacrylate) diblock copolymer, the block copolymer can be annealed at170° C. for four days. In other embodiments, the block copolymer film isannealed by exposure to solvent vapors. For example, when the blockcopolymer is a polystyrene-poly(4-vinylpyridine) diblock copolymer, theannealing solvent vapor can comprise toluene and tetrahydrofuran.

In some embodiments, the annealed block copolymer film comprises ahexagonal array of cylindrical microdomains. Such hexagonal arrays canexhibit an orientation order of at least 0.9 over an area of at least 1centimeter². Orientation order can be determined by image analysis ofscanning force microscopy images of the block copolymer films using, forexample, MATLAB software from The Mathworks. The cylindricalmicrodomains can be separated by a nearest-neighbor distance of about 10to about 100 nanometers.

In some embodiments, the annealed block copolymer film comprises alinear array of microdomains. The center-to-center spacings of thelinear microdomains can be about 10 to about 100 nanometers.

After the block copolymer film is annealed, it is surface reconstructed.The surface reconstruction method is described in T. Xu, C. J. Hawker,and T. P. Russell, Advanced Functional Materials, 2003, volume 13, page698 ff. and typically consists of exposing the annealed block copolymerfilm to a solvent that preferentially dissolves the minor phase of theblock copolymer film and effects transfer of that phase to the surfaceof the film opposite the substrate. It is important to note that nochemical bonds are broken in the surface reconstruction process, andthat the process is reversible (for example, by the application ofheat). Surface reconstruction is conducted at a temperature below theglass transition temperature of the major (matrix) phase of the blockcopolymer film, so that the structure of the film is conserved in thatthe spaces formerly occupied by the minor phase are converted to voids.For example, when the minor phase consists of cylinders perpendicular tothe plane of the film, surface reconstruction results in migration ofthe minor phase to the top surface of the film and formation ofcylindrical voids where the minor phase formerly resided. Thecylindrical voids extend from the substrate surface through the majorphase-containing layer and the minor phase-containing layer to the topof the block copolymer film. As another example, when the minor phaseconsists of lines parallel to the plane of the film, surfacereconstruction results in the migration of the minor phase to the topsurface of the film and formation of linear voids (troughs or trenches)where the minor phase formerly resided.

In some embodiments, the block copolymer is apolystyrene-poly(4-vinylpyridine) diblock copolymer, and surfacereconstructing the annealed block copolymer film comprises immersing theblock copolymer film in a lower alkanol solvent such as methanol,ethanol, 1-propanol, 2-propanol, or a mixture thereof.

FIG. 1 is a schematic illustration of articles associated with thepresent method. FIG. 1(A) shows crystalline substrate 1 comprising anannealed, miscut surface 2 comprising a saw-tooth topology. FIG. 1(B)shows the block copolymer film-coated substrate 10, which is the productof forming a block copolymer film on annealed, miscut surface 2. In FIG.1(B), a block copolymer film 11 is disposed on annealed, miscut surface2 of crystalline substrate 1. The block copolymer film 11 comprises acontinuous phase 12 comprising the major component of the blockcopolymer, and a minor phase comprising cylindrical domains 13comprising the minor component of the block copolymer. FIG. 1(C) showsthe annealed block copolymer film-coated substrate 20, which is theproduct of annealing the block copolymer film 11. The annealed blockcopolymer film-coated substrate 20 comprises crystalline substrate 1 andannealed block copolymer film 21. The annealed block copolymer film 21comprises an annealed continuous phase 22 comprising the major componentof the block copolymer, and an annealed minor phase comprising annealedcylindrical domains 23. The annealed cylindrical domains 23 collectivelyform a hexagonal array of cylindrical domains within the continuousphase 22. The orientation order of the hexagonal array of cylindricaldomains in the annealed block copolymer film 21 is significantly higherthan that of the array of cylindrical domains in the block copolymerfilm 21 immediately after its formation on the annealed, miscut surface2. FIG. 1(D) shows the solvent-reconstructed, annealed block copolymerfilm-coated substrate 30, which is the product of solvent-reconstructingthe annealed block copolymer film-coated substrate 20.Thesolvent-reconstructed, annealed block copolymer film-coated substrate 30comprises crystalline substrate 1 and solvent-reconstructed blockcopolymer film 31. The solvent reconstruction step transfers the minorphase component from the cylindrical domains to the top of the blockcopolymer layer. Thus, the solvent-reconstructed block copolymer film 31comprises a major block layer 32 disposed on the annealed miscut surface2 of the crystalline substrate 1 and composed primarily of the majorcomponent of the block copolymer. The solvent-reconstructed blockcopolymer film 31 further comprises a minor block layer 33, disposed ona surface of the major block layer opposite the annealed miscut surface2 and composed primarily of the minor component of the block copolymer.The major block layer 32 and the minor block layer 33 collectivelydefine an array of cylindrical voids 34, corresponding to spacesremaining when the minor phase of the block copolymer was transferredfrom the annealed cylindrical domains 23 to the top surface of the blockcopolymer film.

In some embodiments, the method further comprises coating anetch-resistant layer on a surface of the surface reconstructed blockcopolymer film to form a resist-coated block copolymer film. Theetch-resistant layer can be coated using various methods known in theart, including, for example, evaporating, sputtering, chemical vapordeposition (CVD), and metalorganic chemical vapor deposition (MOCVD).The etch-resistant layer will generally include at least one materialthat is more etch-resistant than the block copolymer film. Suitablematerials include metals, such as iron, ruthenium, osmium, cobalt,nickel, palladium, platinum, copper, silver, gold, and the like, andalloys of the foregoing. When the etch-resistant layer comprises ametal, the etch-resistant layer can be formed by evaporating the metaland allowing the evaporated metal to deposit on the top surface of theblock copolymer film In some embodiments, including those embodiments inwhich subsequent etching of the substrate is intended, it is desirableto avoid depositing etch-resistant material into the voids formed onsurface reconstruction. In these embodiments, the etch-resistantmaterial is deposited from a glancing angle relative to the plane of theblock copolymer film. In other embodiments, it is desirable to depositetch-resistant material into the voids formed on surface reconstructionso that the etch-resistant material is deposited through the voids ontothe substrate surface. In these embodiments, the etch-resistant materialis deposited from an angle approximately normal to the plane of theblock copolymer film. Although the term “etch-resistant layer” is used,coating the etch-resistant material need not be followed by an etchingstep. For example, when the surface reconstructed block copolymer filmdefines a hexagonal array of cylindrical pores and the etch-resistantmaterial is a magnetic material that is deposited from an angleapproximately normal to the plane of the substrate surface, coating ofthe etch resistant layer can be followed by separation of the blockcopolymer layer from the substrate, yielding a substrate decorated witha hexagonal array of magnetic islands.

In some embodiments, coating the etch-resistant layer on the surfacereconstructed block copolymer film comprises depositing gold onto thesurface reconstructed block copolymer film.

One use of the method is to prepare nanopatterned substrates.Nanopatterned substrates can be prepared by etching through theresist-coated block copolymer film and into the substrate, therebycreating voids in the substrate corresponding to voids in thesurface-reconstructed block copolymer layer. Suitable etching methodsinclude for example, dry chemical etching, wet chemical etching, plasmaetching, reactive ion etching, micromachining, electron beam writing,laser micromachining, ablation, ion beam milling, and the like. In someembodiments, reactive ion etching is used. Suitable precursors forreactive ion etching include, for example, tetrafluoromethane,fluorotrichloromethane, and antimony hexafluoride. In some embodiments,etching the resist-coated block copolymer film comprises reactive ionetching using a tetrafluoromethane precursor. The nanopatternedsubstrate can be separated from the etch-resistant layer and the blockcopolymer film. This separation step can, for example, comprisecontacting the etched article with a solution capable of dissolving orsolubilizing the etch-resistant layer. For example, when theetch-resistant layer comprises gold, suitable solutions include aqueoussolutions comprising potassium iodide and iodine, and aqueous solutionscomprising cyanide ion. In some embodiments, the separation stepcomprises using a so-called lift-off method to swell the block copolymerlayer and separate it and the overlying etch-resistant layer from thesubstrate. Solvents suitable for use in a lift-off method include anysolvent or solvent mixture capable of swelling the block copolymer. Forexample, when the block copolymer is a polystyrene-poly(4-vinylpyridine)diblock copolymer, suitable solvents include toluene, tetrahydrofuran,chloroform, dimethylformamide, dimethylacetamide, and the like, andmixtures thereof The lift-off method can, optionally, comprise agitationor sonication to facilitate separation of the swollen block copolymerlayer from the substrate. In some embodiments, separating theetch-resistant layer and the block copolymer film from the nanopatternedsubstrate comprises contacting the etched article with an aqueoussolution comprising potassium iodide and iodine.

FIG. 2 is a schematic illustration of articles associated with a methodof producing nanopatterned substrate. FIG. 2(A), which is equivalent toFIG. 1(D), shows a solvent-reconstructed, annealed block copolymerfilm-coated substrate 30. The solvent-reconstructed, annealed blockcopolymer film-coated substrate 30 comprises crystalline substrate 1,and solvent-reconstructed block copolymer film 31. Thesolvent-reconstructed block copolymer film 31 comprises major blocklayer 32 disposed on the annealed miscut surface 2 of the crystallinesubstrate 1 and composed primarily of the major component of the blockcopolymer. The solvent-reconstructed block copolymer film 31 furthercomprises a minor block layer 33, disposed on a surface of the majorblock layer opposite the annealed miscut surface 2 and composedprimarily of the minor component of the block copolymer. The major blocklayer 32 and the minor block layer 33 collectively define an array ofcylindrical voids 34, corresponding to spaces remaining when the minorphase of the block copolymer was transferred from the annealedcylindrical domains 23 to the top surface of the block copolymer film.Coating an etch resist layer from a glancing angle ontosolvent-reconstructed, annealed block copolymer film-coated substrate 30produces resist-coated, solvent-reconstructed, annealed block copolymerfilm-coated substrate 40, which is shown in FIG. 2(B). This layeredstructure comprises etch resist layer 41, and substrate 1, major blocklayer 32, minor block layer 33, and voids 34. Etching the resist-coated,solvent-reconstructed, annealed block copolymer film-coated substrate 40produces etched, resist-coated, solvent-reconstructed, annealed blockcopolymer film-coated substrate 50, which is shown in FIG. 2(C). Thislayered structure comprises etched etch-resist layer 51, etched majorblock layer 32, etched minor block layer 53, etched voids 54, and etchedsubstrate 55. Although the etch resistant layer 41 largely protects frometching the major block layer 32, minor block layer 33, and voids 34,some etching of these features can occur in the etching step, hence theyare renumbered in FIG. 2(C) and renamed with the modifier “etched”.

Another use of the method is to prepare arrays of magnetic materials ona substrate. For example, when the surface-reconstructed block copolymerfilm defines a hexagonal array of cylindrical voids extending(perpendicular to and) through the surface-reconstructed block copolymerfilm, a magnetic material can be coated onto and from directly above thesurface reconstructed block copolymer film so that it at least partiallyfills the voids defined by the surface reconstructed block copolymerfilm Suitable magnetic materials include, for example, nickel, cobalt,chromium, and alloys of iron and platinum. Once the magnetic materialhas been coated, the magnetically decorated substrate can be separatedfrom the block copolymer film using, for example, a lift-off method.

In a very specific embodiment of the method, the crystalline substrateconsists essentially of a single crystal of crystalline aluminum oxideor doped silicon; the block copolymer film comprises apolystyrene-block-poly(4-vinylpyridine) diblock copolymer comprising apolystyrene block having a number average molecular weight of about6,000 to about 30,000 atomic mass units and a poly(4-vinylpyridine) orpoly(2-vinylpyridine) block having a number average molecular weight ofabout 2,000 to about 10,000 atomic mass units; a ratio of the numberaverage molecular weight of the polystyrene block to the number averagemolecular weight of the poly(4-vinylpyridine) or poly(2-vinylpyridine)block is about 2 to about 6; the annealing the block copolymer filmcomprises exposing the block copolymer film to an annealing solventvapor comprising toluene and tetrahydrofuran; the annealed blockcopolymer film comprises a hexagonal array of cylindricalpoly(4-vinylpyridine) or poly(2-vinylpyridine) microdomains; thehexagonal array of cylindrical microdomains exhibits an orientationorder of at least 0.9 over an area of at least 1 centimeter; and whereinthe surface reconstructing the annealed block copolymer film comprisesimmersing the annealed block copolymer film in a solvent comprising aC₁-C₃ alkanol. In some embodiments, the method further comprises coatinga gold layer on the surface reconstructed block copolymer film; whereinthe gold layer has a thickness of about 0.5 to about 2 nanometers.

In another very specific embodiment of the method, the crystallinesubstrate consists essentially of a single crystal of crystallinealuminum oxide or doped silicon; the block copolymer film comprises apolystyrene-block-poly(ethylene oxide) diblock copolymer comprising apolystyrene block having a number average molecular weight of about6,000 to about 30,000 atomic mass units and a poly(ethylene oxide) blockhaving a number average molecular weight of about 2,000 to about 10,000atomic mass units; a ratio of the number average molecular weight of thepolystyrene block to the number average molecular weight of thepoly(ethylene oxide) block is about 2 to about 6; the annealing theblock copolymer film comprises exposing the block copolymer film to anannealing solvent vapor comprising toluene and tetrahydrofuran; theannealed block copolymer film comprises a hexagonal array of cylindricalpoly(ethylene oxide) microdomains; the hexagonal array of cylindricalmicrodomains exhibits an orientation order of at least 0.9 over an areaof at least 1 centimeter; and wherein the surface reconstructing theannealed block copolymer film comprises immersing the annealed blockcopolymer film in a solvent comprising a C₁-C₃ alkanol. In someembodiments, the method further comprises coating a gold layer on thesurface reconstructed block copolymer film; wherein the gold layer has athickness of about 0.5 to about 2 nanometers.

The invention includes layered articles prepared by the above-describedmethods. The method's ability to generate highly ordered arrays overlarge areas permits the fabrication of memory devices. For example, thememory devices can be fabricated by a method comprising depositingmagnetic material in the voids formed by surface reconstruction of anannealed block copolymer film comprising a hexagonal array ofcylindrical domains. Due to the small separations of microdomains in theannealed block copolymer films, the memory device can have a very highstorage density. For example, in some embodiments, the memory device hasan areal storage density of about 1×10¹⁰ to about 1.5×10¹² bits persquare centimeter. In addition to their use in the fabrication of memorydevices, the long-range lateral order of the nanopatterned articlesmakes them useful for applications such as polarizers (for background,see V. Pelletier, K. Asakawa, M. Wu, D. H. Adamson, R. A. Register, andP. M. Chaiken, Applied Physics Letters, 2006, volume 88, page 211114ff.), templates for pattern transfer to generate microelectronicintegrated circuits (for background, see C. T. Black, IEEE Transactionson Nanotechnology, 2004, volume 3, page 412 ff.), magnetic media (forbackground, see, for example, C. A. Ross, Annual Review of MaterialsResearch, 2001, volume 31, page 203 ff.), and optical waveguides (forbackground, see C. A. Ross, Annual Reviews of Materials Research, 2001,volume 31, page 203 ff.; and S. A. Maier, M. L. Brongersma, P. G. Kik,S. Meltzer, A. A. G. Requicha, and H. A. Atwater, Advanced Materials,2001, volume 13, page 1501 ff.).

One embodiment is a layered article, comprising: a crystalline substratecomprising an annealed, miscut surface; and a block copolymer filmdisposed on the annealed, miscut surface; wherein the block copolymerfilm comprises a block copolymer comprising a first block and a secondblock; wherein the block copolymer film comprises a major block layercontacting the annealed, miscut surface, and comprising at least 65weight percent, specifically 65 to 85 weight percent, of the firstblock, and a minor block layer contacting the major block layer (andopposite from the substrate), and comprising at least 80 weight percentof the second block; and wherein the block copolymer film defines ahexagonal array of cylindrical voids extending (perpendicular to and)through the major block layer and the minor block layer. Such a layeredarticle can be formed by a process comprising forming a block copolymerfilm on an annealed, miscut surface of a crystalline substrate;annealing the block copolymer film; and surface reconstructing theannealed block copolymer film. The layered article can, optionally,further comprise an etch resist layer disposed on the minor block layerof the block copolymer film (opposite the major block layer of the blockcopolymer film)

The invention includes at least the following embodiments.

Embodiment 1: A method of preparing a nanopatterned surface, comprising:forming a block copolymer film on an annealed, miscut surface of acrystalline substrate; annealing the block copolymer film; and surfacereconstructing the annealed block copolymer film.

Embodiment 2: The method of embodiment 1, wherein the annealed blockcopolymer film comprises a hexagonal array of cylindrical microdomains.

Embodiment 3: The method of embodiment 2, wherein the hexagonal array ofcylindrical microdomains exhibits an orientation order of at least 0.9over an area of at least 1 centimeter.

Embodiment 4: The method of embodiment 2 or 3, wherein the cylindricalmicrodomains are separated by a nearest-neighbor distance of about 10 toabout 100 nanometers.

Embodiment 5: The method of embodiment 1, wherein the annealed blockcopolymer film comprises a linear array of microdomains.

Embodiment 6: The method of any of embodiments 1-5, wherein the blockcopolymer comprises a first block having a first Hildebrand solubilityparameter and a second block having a second Hildebrand solubilityparameter, and wherein the first Hildebrand solubility parameter and thesecond Hildebrand solubility parameter differ by at least 0.4megapascar.

Embodiment 7: The method of embodiment 6, wherein the first block andthe second block differ in number average molecular weight by at least afactor of 1.5.

Embodiment 8: The method of any of embodiments 1-7, wherein the blockcopolymer is a polystyrene-poly(4-vinylpyridine) orpolystyrene-poly(2-vinylpyridine) diblock copolymer.

Embodiment 9: The method of any of embodiments 1-7, wherein the blockcopolymer is a polystyrene-poly(ethylene oxide) diblock copolymer.

Embodiment 10: The method of any of embodiments 1-9, wherein the blockcopolymer film has a thickness of about 10 to about 100 nanometers.

Embodiment 11: The method of any of embodiments 1-10, wherein thecrystalline substrate consists essentially of a single crystal.

Embodiment 12: The method of any of embodiments 1-11, wherein thecrystalline substrate is selected from the group consisting ofcrystalline silicon, doped crystalline silicon, and crystalline aluminumoxide.

Embodiment 13: The method of any of embodiments 1-12, wherein thecrystalline substrate comprises crystalline silicon.

Embodiment 14: The method of any of embodiments 1-12, wherein thecrystalline substrate comprises crystalline aluminum oxide.

Embodiment 15: The method of any of embodiments 1-14, wherein the miscutcrystalline surface is at least one degree removed from anycrystallographic plane of the crystalline substrate.

Embodiment 16: The method of any of embodiments 1-15, wherein theannealed, miscut surface of the crystalline substrate exhibits asaw-tooth pattern characterized by a peak-to-peak separation of about 24to about 200 nanometers and a peak-to-valley separation of about 3 toabout 20 nanometers.

Embodiment 17: The method of any of embodiments 1-15, wherein theannealed, miscut surface of the crystalline substrate exhibits a groovedpattern characterized by a groove depth of about 3 to about 20nanometers and a groove-to-groove separation of about 24 to about 200nanometers.

Embodiment 18: The method of any of embodiments 1-17, wherein theannealed, miscut surface of the crystalline substrate is chemicallyhomogeneous.

Embodiment 19: The method of any of embodiments 1-8, wherein the blockcopolymer is a polystyrene-poly(4-vinylpyridine) diblock copolymer, andwherein the surface reconstructing the annealed block copolymer filmcomprises immersing the block copolymer film in a lower alkanol solventselected from the group consisting of methanol, ethanol, and mixturesthereof.

Embodiment 20: The method of any of embodiments 1-19, further comprisingcoating an etch-resistant layer on the surface reconstructed blockcopolymer film to form a resist-coated block copolymer film.

Embodiment 21: The method of embodiment 20, wherein the coating theetch-resistant layer on the surface reconstructed block copolymer filmcomprises depositing gold onto the surface reconstructed block copolymerfilm.

Embodiment 22: The method of embodiment 20 or 21, further comprisingetching through the resist-coated block copolymer film and into thesubstrate to create an etched article comprising a nanopatternedsubstrate.

Embodiment 23: The method of embodiment 22, further comprisingseparating the etch-resistant layer and the block copolymer film fromthe nanopatterned substrate.

Embodiment 24: The method of embodiment 1, wherein thesurface-reconstructed block copolymer film defines a hexagonal array ofcylindrical voids extending through the surface-reconstructed blockcopolymer film; and wherein the method further comprises coating amagnetic material on the surface reconstructed block copolymer film andinto the voids defined by the surface reconstructed block copolymerfilm.

Embodiment 25: The method of embodiment 24, wherein the magneticmaterial is selected from the group consisting of nickel, cobalt,chromium, and alloys of iron and platinum.

Embodiment 26: The method of embodiment 24 or 25, further comprisingseparating the magnetic material-coated, reconstructed block copolymerfilm from the crystalline substrate to form a miscut surface decoratedwith a hexagonal array of magnetic islands.

Embodiment 27: The method of embodiment 1, wherein the crystallinesubstrate consists essentially of a single crystal of crystallinealuminum oxide or doped silicon; wherein the block copolymer filmcomprises a polystyrene-block-poly(4-vinylpyridine) diblock copolymercomprising a polystyrene block having a number average molecular weightof about 6,000 to about 30,000 atomic mass units and apoly(4-vinylpyridine) or poly(2-vinylpyridine) block having a numberaverage molecular weight of about 2,000 to about 10,000 atomic massunits; wherein a ratio of the number average molecular weight of thepolystyrene block to the number average molecular weight of thepoly(4-vinylpyridine) or poly(2-vinylpyridine) block is about 2 to about6; wherein the annealing the block copolymer film comprises exposing theblock copolymer film to an annealing solvent vapor comprising tolueneand tetrahydrofuran; wherein the annealed block copolymer film comprisesa hexagonal array of cylindrical poly(4-vinylpyridine) orpoly(2-vinylpyridine) microdomains; wherein the hexagonal array ofcylindrical microdomains exhibits an orientation order of at least 0.9over an area of at least 1 centimeter²; and wherein the surfacereconstructing the annealed block copolymer film comprises immersing theannealed block copolymer film in a solvent comprising a C₁-C₃ alkanol.

Embodiment 28: The method of embodiment 1, wherein the crystallinesubstrate consists essentially of a single crystal of crystallinealuminum oxide or doped silicon; wherein the block copolymer filmcomprises a polystyrene-block-poly(ethylene oxide) diblock copolymercomprising a polystyrene block having a number average molecular weightof about 6,000 to about 30,000 atomic mass units and a poly(ethyleneoxide) block having a number average molecular weight of about 2,000 toabout 10,000 atomic mass units; wherein a ratio of the number averagemolecular weight of the polystyrene block to the number averagemolecular weight of the poly(ethylene oxide) block is about 2 to about6; wherein the annealing the block copolymer film comprises exposing theblock copolymer film to an annealing solvent vapor comprising tolueneand tetrahydrofuran; wherein the annealed block copolymer film comprisesa hexagonal array of cylindrical poly(ethylene oxide) microdomains;wherein the hexagonal array of cylindrical microdomains exhibits anorientation order of at least 0.9 over an area of at least 1centimeter²; and wherein the surface reconstructing the annealed blockcopolymer film comprises immersing the annealed block copolymer film ina solvent comprising a C₁-C₃ alkanol.

Embodiment 29: A layered article prepared by the process of embodiment1.

Embodiment 30: The layered article of embodiment 29, wherein the layeredarticle is a memory device.

Embodiment 31: The layered article of embodiment 30, wherein the memorydevice has an areal storage density of about 1×10¹⁰ to about 1.5×10¹²bits per square centimeter.

Embodiment 32: A layered article, comprising: a crystalline substratecomprising an annealed, miscut surface; and a block copolymer filmdisposed on the annealed, miscut surface; wherein the block copolymerfilm comprises a block copolymer comprising a first block and a secondblock; wherein the block copolymer film comprises a major block layercontacting the annealed, miscut surface, and comprising at least 65weight percent of the first block, and a minor block layer contactingthe major block layer, and comprising at least 80 weight percent of thesecond block; and wherein the block copolymer film defines a hexagonalarray of cylindrical voids extending through the major block layer andthe minor block layer.

Embodiment 33: The layered article of embodiment 32, further comprisingan etch resist layer disposed on the minor block layer of the blockcopolymer film.

The invention is further illustrated by the following non-limitingexamples.

WORKING EXAMPLES

Preparation of miscut silicon substrate. The miscut silicon substrateswere polished silicon wafers with the surface normal pointing 2 to 4degrees off the <113> crystal axis toward the <001> axis. These miscutsilicon substrates were obtained from University Wafer as miscut siliconwafers. Arsenic doped (n-type) silicon was used to enable resistiveheating. The miscut silicon wafers were repeatedly heated underultrahigh vacuum conditions (that is, a pressure less than 1×10⁻⁹ torr(0.13 micropascal)) by flowing a direct current through them. They weremaintained at a temperature of 1535 K (1262° C.) for one minute, thenrapidly cooled to 1300 K (1027° C.), then slowly cooled to roomtemperature and exposed to ambient conditions.

Preparation of miscut sapphire substrate. Miscut C-plane sapphire(miscut inclination angle of several degree towards the [1 1 00]direction) was annealed in air at 1373 K (1100° C.) for 10 hours.M-plane sapphire, which is not a miscut surface but is instead anunstable plane formed at temperatures over 1200° C., was formed byheating a sapphire wafer in air at 1300 to 1500° C. for 24 hours to formself-generated saw-tooth patterns. Typically, such annealed sapphiresubstrates exhibit a saw-tooth topography with a peak-to-valleyseparation of about 10 nanometers and average peak separation distanceranging from about 70 to about 200 nanometers. A scanning forcemicroscope image of a 5 micrometer×5 micrometer area of an annealedsapphire substrate is presented as FIG. 3.

Development of block copolymer thin film onto grooved surface.Polystyrene-block-poly(ethylene oxide) (PS-b-PEO) was dissolved inbenzene at room temperature, whilepolystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymerswere dissolved in toluene/tetrahydrofuran solvent mixtures at 70° C. for2 hours and cooled to room temperature. Block copolymer thin films werefabricated by spin-coating typically at 3,000 rotations per minute (rpm)and 60 seconds from a 0.7-1.0 weight percent solution onto thegroove-patterned surface of a sapphire substrate that had previouslybeen cleaned using oxygen plasma. Cylindrical microdomains normal to thesurface formed spontaneously after spin-coating. Annealing the resultingfilms with solvent vapor produced an array of cylindrical microdomainswith a high degree of lateral order

Solvent annealing of PS-b-PEO was performed in water vapor for 1 hour,followed by benzene/water vapor environment for 4 hours at roomtemperature. In contrast, PS-b-P4VP was annealed in the vapor of atoluene/tetrahydrofuran solvent mixture (toluene: tetrahydrofuranvolume/volume ratio about 20:80 to about 80:20) for 10 hours at roomtemperature. After solvent annealing of PS-b-PEO and PS-b-P4VP, theorientational order of cylindrical microdomains is typically over 0.90.

Surface reconstruction of solvent annealed films was conducted bydipping the films into methanol or ethanol for 20 minutes, followed bydrying in a nitrogen atmosphere. This surface reconstruction processthat moves PEO or P4VP from the cylindrical domains to the surface ofthe film, creating nanopores in the block copolymer film FIG. 4 shows anSFM image of a polystyrene-block-poly(ethylene oxide) (PS-b-PEO; numberaverage molecular weight of PS block is about 20,000 atomic mass units;number average molecular weight of poly(ethylene oxide) is about 6,500atomic mass units) block copolymer thin film annealed in benzene/watervapor on a saw-tooth-patterned annealed sapphire substrate. Thesaw-tooth pattern of the sapphire substrate guides the long-range orderof cylindrical microdomains oriented normal to the film surface. Highlyordered microdomains are shown in the SFM image, and the Fouriertransform pattern (FIG. 4 inset) shows multiple order scattering spots,which are characteristic of long-range order. From image analysis, anaverage cylindrical microdomain diameter of about 27 nanometers and anaverage center-to-center distance of about 56 nanometers werecalculated.

To decrease the feature size and center-to-center distance ofcylindrical microdomains, a smaller molecular weight of PS-b-PEO blockcopolymer was used. The polystyrene block had a number average molecularweight of about 16,000 atomic mass units, and the poly(ethylene oxide)block had a number average molecular weight of about 3,500 atomic massunits. Highly ordered cylindrical microdomains oriented normal to thesurface are shown in FIG. 5. The smaller molecular weight PS-b-PEOsystem was developed at slightly different annealing condition comparingwith the higher molecular weight PS-b-PEO. Higher molecular weightPS-b-PEO was annealed in benzene/water vapor for 4 hours, while lowermolecular weight PS-b-PEO was annealed for 3 hours. Even though use oflower molecular weight PS-b-PEO led to the formation of smallermicrodomains, their long range order was guided by thesaw-tooth-patterned annealed sapphire surface. From image analysis, anaverage cylindrical microdomain diameter of about 16 nanometers, and anaverage center-to-center distance of about 30 nanometers werecalculated.

Gold decoration and reactive ion etching of block copolymer thin filmsTo transfer the pattern produced by the gold coated polymer films intothe underlying substrate, the films were etched using reactive ionetching (RIE) under SF₆ atmosphere (TRION technology, at 50 millitorrpressure, 25 standard cubic centimeter per minute flow rate, and 40watts power). After etching into the silicon oxide, the gold coatedfilms were removed with a 10 wt % KI/I₂ (4/1, volume/volume) solution,followed by oxygen plasma etching for 10 minutes. FIG. 6 showstransferred patterns of three gold decorated polymer templates intosilicon oxide using SF₆ RIE with high fidelity. It should be noted thatthe metal coated films can be used as hard etching masks for patterntransfer into the underlying substrate. Etching can be either positiveor negative. FIG. 6(A) shows a silicon oxide surface with nano-sizedpores, and FIG. 6(B) shows a silicon oxide surface with nano-sizedpillars. The scale bar in each image is 100 nanometers.

To get much higher areal density of cylindrical micro domains,polystyrene-block-poly(ethylene oxide) (molecular weights of polystyreneand poly(ethylene oxide) are 16,000 and 5,000 atomic mass units,respectively) thin films were annealed in xylene vapor for 2 hours atroom temperature. Highly ordered cylindrical microdomains having anaverage separation distance of about 20.9 nanometers and a circulardomain size of about 7.8 nanometers, corresponding to an areal densityof about 0.38 terabit per square centimeter, can be seen in FIG. 7. FIG.7 shows annealed (but not solvent reconstructed)polystyrene-block-poly(ethylene oxide) films on annealed, miscutsapphire substrates. The substrate used to generate FIG. 7 was annealedin xylene vapor for 2 hours at room temperature.

Comparison of block copolymer films on unpatterned and patternedsapphire substrates. To characterize the grain size and orientation ofPEO cylindrical microdomains, the Moire interference pattern analysiswas used. Long-range order is shown in larger area (25 micrometer×25micrometer) Moire interference patterns. When the same PS-b-PEO thinfilms are developed at the same annealing condition onto flat sapphiresubstrate, multi-grain, a number of defects and dislocation wereobserved from the Moire interference pattern as shown in FIG. 8. FIG. 8shows Moire patterns on annealed (but not solvent reconstructed)polystyrene-block-poly(ethylene oxide) films on flat M-plane sapphire(FIG. 8(A); unpatterned surface) and miscut sapphire (FIG. 8(B);patterned surface) substrates.

Characterization of Block Copolymer Films by Grazing IncidenceSmall-Angle X-ray Scattering. To characterize the nanostructures ofblock copolymer over a larger area, we employed grazing incidencesmall-angle X-ray scattering (GISAXS). GISAXS was used to investigatethe morphology of the PS-b-PEO and its orientation within the samples.FIG. 9 shows two dimensional GISAXS patterns of PS-b-PEO thin films FIG.9(A) represents the hexagonal cylinder viewed from the direction ofcylindrical axes, the (10) symmetric plane. GISAXS patterns ofcylindrical microdomains show only integer diffraction peaks from (10)symmetric plane. As shown in FIG. 9(B), when the sample stage is rotatedto 30 degrees from the (01) symmetric plane, diffraction peaks from(10), (11), (20), (21), (30), and (22) symmetric plane appeared.Depending upon whether the lattice of cylindrical microdomains ismatched with the (10) symmetric plane, integer or hexagonal diffractionpeaks were seen. These results demonstrate that saw-tooth patterns inmiscut crystalline substrates can guide the PS-b-PEO cylindricalmicrodomains over at least a 1.5 centimeter×1.5 centimeter area,creating nearly perfect registry of the domains over that area.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to make and use the invention. The patentable scope of the inventionis defined by the claims, and may include other examples that occur tothose skilled in the art. Such other examples are intended to be withinthe scope of the claims if they have structural elements that do notdiffer from the literal language of the claims, or if they includeequivalent structural elements with insubstantial differences from theliteral language of the claims.

All cited patents, patent applications, and other references areincorporated herein by reference in their entirety. However, if a termin the present application contradicts or conflicts with a term in theincorporated reference, the term from the present application takesprecedence over the conflicting term from the incorporated reference.

All ranges disclosed herein are inclusive of the endpoints, and theendpoints are independently combinable with each other.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. Further, it should further be noted that the terms “first,”“second,” and the like herein do not denote any order, quantity, orimportance, but rather are used to distinguish one element from another.The modifier “about” used in connection with a quantity is inclusive ofthe stated value and has the meaning dictated by the context (e.g., itincludes the degree of error associated with measurement of theparticular quantity).

1. A layered article prepared by a method comprising: forming a blockcopolymer film on an annealed, miscut surface of a crystallinesubstrate; wherein the block copolymer film comprises a major phase anda minor phase; and wherein the block copolymer film comprises a bottomsurface in contact with the annealed, miscut surface of the crystallinesubstrate, and a top surface not in contact with the annealed, miscutsurface of the crystalline substrate; annealing the block copolymerfilm; and surface reconstructing the annealed block copolymer film sothat the minor phase migrates to the top surface of the block copolymerfilm, thereby forming voids in the block copolymer film
 2. The layeredarticle of claim 1, wherein the layered article consists of thecrystalline substrate and the solvent-reconstructed block copolymer film3. The layered article of claim 1, wherein, after said annealing, theminor phase consists of lines parallel to the plane of the film, andwherein said surface reconstruction results in the formation of linearvoids in the block copolymer film
 4. The layered article of claim 1,wherein, after said annealing, the minor phase consists of cylindersperpendicular to the plane of the block copolymer film, and wherein saidsurface reconstruction results in formation of cylindrical voids in theblock copolymer film
 5. The layered article of claim 4, wherein themethod further comprises coating a resist from a glancing angle onto thesolvent-reconstructed block copolymer film to form an article comprisingthe substrate, the solvent-reconstructed block copolymer film, and aresist layer; and etching the article onto and perpendicularly to theresist layer to form cylindrical voids in the substrate.
 6. The layeredarticle of claim 4, wherein the method further comprises depositing amagnetic material perpendicularly onto the top surface of thesolvent-reconstructed block copolymer film and through the pores of thesolvent-reconstructed block copolymer film onto the substrate to yieldan article comprising a magnetically-decorated substrate and amagnetically-coated block copolymer film; and separating themagnetically-coated block copolymer film from the magnetically-decoratedsubstrate.
 7. The layered article of claim 6, wherein the article is themagnetically-decorated substrate; and wherein the magnetically-decoratedsubstrate is a memory device having an areal storage density of about1×10¹⁰ to about 1.5×10¹² bits per square centimeter.